(sī-fŏn'ə-fôr', sī'fə-nə-) Any of various transparent, often subtly colored marine cnidarians of the order Siphonophora, consisting of a delicate floating or swimming colony of polyplike and medusalike individuals. Siphonophores can reach lengths of 40 m (131 ft), making them longer than blue whales. The Portuguese man-of-war is a siphonophore.